When someone says "spring to mind," they usually mean that a certain thought or idea has just popped into their head. This phrase can be replaced with a wide variety of synonyms, depending on the context of the sentence. For instance, someone might say "came to mind" or "occurred to me" instead. Alternatively, someone might say "hit me" or "dawned on me" to convey a similar idea. Depending on the tone and level of surprise, "popped into my head" or "leapt to mind" might be more appropriate. Ultimately, there are many options to choose from when replacing this phrase, depending on what feels natural in the moment.